Over $300,000 has been raised as a reward for information that leads to the arrest and conviction of a suspect involved in an explosion in downtown Nashville on Christmas morning.

Authorities are calling the bombing “an intentional act” and have found possible human remains in the area. The bomb detonated inside an RV parked on historic Second Avenue near Lower Broadway, injuring three people including a police officer.

No known suspects or motive behind the blast have been announced.

“We will find out who did this,” FBI Special Agent Matt Foster said during a news conference.

“This is our city, too. We’re putting everything we have into finding who was responsible for what happened here today.”

The FBI’s Memphis field office is investigating along with local officials and the Bureau of Alcohol, Tobacco, Firearms and Explosives, and the city of Nashville activated its Emergency Operations Center.

A spokesperson for the Department of Justice said Acting Attorney General Jeff Rosen “directed that all DOJ resources be made available to assist in the investigation.”

“We’re putting everything we have into finding who was responsible for what’s happened here today,” Foster said.

Metro Nashville Police Department Chief John Drake told reporters that authorities do not believe there is any further risk “to the downtown area.”

The RV blew up at approximately 6:30 a.m. central yesterday.

It was unclear whether remains located near the site belong to a victim of the explosion or if they were of the person responsible. Forensic experts will examine the tissue, according to authorities.

An audio warning was broadcast from the RV just before it blew up, Drake said at the news conference.

“If you can hear this message, evacuate now,” the warning said.

Officers first responded to the area after receiving a report of shots fired, Drake said. They called in the bomb squad after seeing the suspicious vehicle, the RV, broadcasting the message, which some witnesses believe included the gunshot sounds.

Officers found the RV as the message said the bomb inside would explode in 15 minutes.

The message said the bomb was going to detonate within a certain time frame. The officers immediately began knocking on doors and evacuating residents here not knowing if the bomb was going to detonate immediately or if it was going to go off in the time that it stated.

As of late yesterday, police did not know if anyone had been inside the vehicle at the time of the explosion.

The injured people were in stable condition, Mayor John Cooper said. At least 41 area businesses and several homes were damaged. Several residents were displaced, Fire Chief William Swann said.